Electronic appliance for setting and checking electronic yarn clearers

ABSTRACT

An electronic apparatus for setting and checking electronic yarn clearer systems, comprising a controllable d.c. amplifying channel having a signal input terminal and at least one control input terminal; a negative feedback loop operatively coupled to said controllable d.c. amplifying channel for compensating for a signal level representing a constant base signal produced by a yarn sensing means of said electronic yarn clearer, said negative feedback loop comprising a switch and a condenser for holding or storing temporarily a compensation potential.

ilmited States Patent 1191 Stutz Sept. 11, 1973 [54] ELECTRONIC APPLIANCE FOR SETTING 3,631,354 12/1971 Werffeli 28/64 AND CHECKING ELECTRONIC YARN 3,303,698 2/1967 Loepfe..... 28/64 CLEARERS 3,476,329 11/1969 Felix 28/64 3,390,441 7/1968 Felix 28/64 Hansruedi Stutz, Dietlikon, Switzerland Assignee: Aktiengesellschaft Gebrudcr Loepfe,

Zurich, Switzerland Filed: Apr. 21, 1972 Appl. No.: 246,303

Inventor:

Foreign Application Priority Data May 27, 1971 Switzerland 7674/71 us. Cl. 356/200, 28/64, 250/219 DF,

. 356/159 Int. Cl. G0ln 21/32, DOlh 13/22 Field of Search 356/199, 200, 159, 356/160; 28/64; 250/219 or; 73/160; 324/61 References Cited UNITED STATES PATENTS 60 12/1970 Fcrtig 356/200 Primary Examiner-David Schonberg Assistant Examiner-V. P. McGraw Attorney-Werner W. Kleeman [57] ABSTRACT An electronic apparatus for setting and checking electronic yarn clearer systems, comprising a controllable d.c. amplifying channel having a signal input terminal and at least one control input terminal; a negative feedback ioop operatively coupled to said controllable d.c. amplifying channel for compensating for a signal level representing a constant base signal produced by a yarn sensing means of said electronic yarn clearer, said negative feedback loop comprising a switch and a condenser for holding or storing temporarily a compensation potential.

13 Claims, 3 Drawing Figures ELECTRONIC APPLIANCE FOR SETTING AND CHECKING ELECTRONIC YARN CLEARERS BACKGROUND OF THE INVENTION The present invention relates to a new electronic apparatus for setting and checking electronic yarn clearers which include means for sensinga yarn contactlessly and for providing a sensing signal, and signal processing means operatively connected to the output of said yarn sensing means, the signal processing means comprising at least one processing channel including a control channel and a signal amplifying channel controllably connected to the control channel, and further comprising threshold discriminating means operatively connectedin series with said signal channel or channels, respectively. 1

Electronic yarn clearers of this general type are known in the art, and specific embodiments of same are described in Swiss Pat. No. 448,836 and in Loepfe- Revue 6/1967. Such plural channel clearers can beset for any kind of yarn in practical use and thus allow of a high degree of clearing.

These'and other yarn clearers known in the art cornprise a contactlessly working yarn sensing device and a thereto coupled a.c. amplifier. A yarn clearer of this type is capable of detecting short-time changes of the yarn sensing signal, however, is unable to determine the long-time mean value thereof which represents the yarn diameter or other transversal dimension of the yarn. Nevertheless, knowledge of such a transversal or transverse dimension is important for pre-setting the yam clearer in a fast and approximately exact manner.

said transversal dimension when pre-setting a yarn clearer. However, the sensing method (optical, capacitive) and the geometrical arrangement of the sensing space comprised in the yarn sensing means play a decisive role in the detection of the yarn dimensions by an electronic yarn clearer. Thus, with the opticalmethod, the determinants colour and structure of the yarn, and with the capacitive method, the material (wool, cotton, synthetics) and the humidity of the yarn have a considerable effect on the measurements. Moreover, the geometry of the sensing space of the yarn sensing means essentially defines the kind of the transversa'l dimension, i.e., by way of example, the diameter, the crosssectional area or the volume of the yarn section located in the sensing space. The aforesaid determinants can be considered, as far as this is possible, by introducing individual corrections, when setting the yarn clearer on the basis of the yarn number or count. Therewith, the setting process becomes not only more complicated, but also setting errors may arise.

' SUMMARY OF THE INVENTION.

Therefore, it is a primary object of the invention to provide a novel apparatus for setting electronic yarn clearers of the aforementioned type which apparatus method inherentin said yarn clearer, and for introducing the thereby determined transversal dimension into theyarn clearer. By the novel apparatus and the abovementioned setting procedure it is possible to avoid the deficiencies of the known setting methods based on the yarn number or count. The novel setting apparatus may also be utilized for checking the operations of a plurality of yarn sensing devices and yarn clearers of similar construction and mode of operation.

In order to implement the aforementioned objectives and others which will become more readily apparent as the prescription proceeds, the preferred embodiment of setting apparatus of the invention comprises a controllable d.c. amplifiying channel having a signal input terminal connectable with the output of the yarn sensing means, and .a control input terminal connectable selectively to any one of the control channels of an electronic multichannel yarn clearer, means connected to the controllable d.c. amplifying channel for compensating for a signal level representing the constant base signal of the sensing signal generated by said yarn sensing means, and indicating means connected to the output of the controllable amplifying channel.

By the setting apparatus of the invention, the idea is realized to duplicate within said apparatus one of the original signal amplifying channels of the electronic yarn clearer at a time and to control each duplicated signal amplifying channel in parallel with the corresponding original signal amplifying channel by the associated control channel comprised in the signal processingmeans of the yarn clearer, in such a way that the amplification of the original signal amplifying channel to be set and the threshold response of same can be reproduced exactly in the controllable d.c. amplifier channel of the setting and checking apparatus.

The electronic yarn clearer to be set may be provided with a photo-electrical yarn .sensing device arranged, together with a yarn severing device, in one and th same unit or feeler head.

With the help of the setting apparatus of the invention it is possible to perform the setting of the individual channels of a multichannel electronic yarn clearer firstly in an objective, secondly in an exact and thirdly in a relatively easy and quick manner, and moreover, to check the various yarn sensing devices and electronic channels of an electronic yarn clearer system with respect to their settings and operation modes.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is'a schematic block diagram of an electronic yarn clearer equipment comprising a feeler head, an

.electronic signal processor and an electronic setting and checking apparatus;

FIG. 2 is a block circuit diagram showing the arrangement of the operational elements comprised by the electronic signal processor and the setting and checking apparatus shown in FIG. 1; and

FIG. 3 is a schematic front view of an equipment for setting electronic yamplearer systems.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the drawings, the electronic yarn clearer illustrated in FIG. I comprises a signal processor 1 including three setting devices C, D, N schematically shown as circles, and a feeler head 3 comprising a yarn severing device 4 and a yarn sensing device 5 which may be a photoelectrical device as known in the art. The output of the yarn sensing device 5 is connected to the input of the signal processor 1, and the yarn severing device 4 is connected to an output of said signal processor 1. The setting devices C, D, N act upon three individual control channels comprised in the signal processor 1 as will be explained in detail with reference to FIG. 2. The said control channels provide three control signals C, D, N the values of which depend upon the settings of the setting devices C, D, N, respectively. The control signals C', D, N are fed to three individual signal amplifying channels of the signal processor l as will be shown in connection with FIG. 2.

The electronic setting and checking apparatus 2 forms a structural unit and comprises a channel selec tor 6, a controllable d.c. amplifier channel 7, an indicating device 8, e.g. a voltmeter connected to the output of the controllable d.c. amplifier channel 7, a compensating and holding circuit 9 connected operatively to the latter, a testing contact or throw-over switch 27 and a testing signal source 28. A sensing signal S provided by the yarn sensing device is led to a signal input A of the amplifier channel 7 through the testing contact 27. The control signals C, D, N are delivered to the channel selector 6; the control signal which is selected by the setting of the channel selector 6 is fed to a control input terminal B of the amplifier channel 7 in order to control the amplification of the latter proportionally to the amplification of the selected signal channel in the signal processor 1. With reference to FIG. 1, the input of the compensating and holding circuit 9 is connected to a second output terminal E of the amplifier channel 7. The output of the compensating and holding circuit 9 is connected to a compensation input terminal K of the amplifier channel 7.

For testing the electronic signal processor 1 the testing signal source 28 which provides for a constant testing signal is connected, by changing over the testing contact 27, to the input terminal A of the amplifying channel 7. The selected control channel is set, by means of the one setting device C resp. D resp. N which is associated therewith in such a manner that the indication at the indicating device 8 corresponds with a fixed index mark M shown in FIG. 2. For testing the feeler head 3, a standardized gauge wire is inserted in the yarn sensing device 5 in the place of a yarn, after switching the testing contact to the position shown in FIG. 1. Thereafter, the indicating device 8 should have the same reading as with the testing signal.

FIG. 2 general description In the upper part of FIG. 2 the circuitry comprised by the signal processor 1 is illustrated by its operational components. The left hand section thereof comprises three control channels S1, S2, S3 and forms the control device of the yarn clearer. The right hand section of the signal processor forms a signal amplifier and comprises three signal channels K1, K2, K3 having different amplifications which are controlled each by one of the said control channels. Thus the signal processor 1 comprises three individual through channels, namely a C- channel or double yarn channel Sl-Kl, an N-channel or nep channel SZ-KZ, and a D-channel S3-K3 which defines the threshold value of the yarn diameter at which the length measurement of the rare yarn imperfections commences.

A signal pre-amplifier SA to which the sensing signal S from the yarn sensing device 5 is delivered, is associated to the three signal channels Kl, K2, K3 commonly. A common threshold discriminator DI is connected operatively in series with the outputs of the three signal channels. Every time the output signal of one of the signal channels reaches the threshold of discrimination DI the latter responds and generates a severing signal T actuating the yarn severing device 4, FIG. I, for eliminating a disturbing yarn imperfection. The magnitudes of the control signals C, D, N which are adjusted by means of the setting devices C, D, N define the amplifications of the signal channels K1, K2, K3 and thus the lower limits for the yarn imperfections to be eliminated.

In the lower part of FIG. 2 the operational block diagram of the electronic control device 2 is represented. The latter comprises the controllable d.c. amplifier channel 7 and the indicating device 8 connected to the output of the amplifier channel 7. The indicating device 8 is, by way of example, a pointer instrument and has two index marks M and MS, the latter marking the full scale reading and the former an intermediate reading, e.g. 7-0 percent of the full scale reading. The sensitivity of the indicating device 8 is such that the full scale reading MS will be reached when one of the output signals of the signal channels in processor 1 reaches the threshold level of the threshold discriminator DI. The amplifier channel 7 is designed in such a manner that its amplification with any value of the control signal, e.g. C, which exists at its control input terminal B corresponds to the amplification of the associated signal channel, e.g. Kl, of the processor ll. That means that the full scale reading of the indication device 8 is reached every time a severing signal T occurs.

In the following description the electronic circuits shown in FIG. 2 will be explained. Since the three channels of processor 1 for their most part are similar with respect to general structure, in the following only the C-channel will be described insofar and in the first place.

The setting device C comprises a potentiometer to which a fixed potential V is applied. A common pulse generator PG is provided for the three control channels S1, S2, S3 to generate a train of rectangular pulses having a repetition rate, by way of example, of 30 kilocycles per second. A pulse duration modulator or modulation circuit PDM is supplied at its one input, with the pulse train from PG, and at its other input with a potential VC tapped off the potentiometer C. The duration of the pulses which appear at the output of PDM is proportional to the potential VC. These pulses are led to a control amplifier CA delivering at its output the control signal C in the shape of a train'of rectangular pulses.

As mentioned in the foregoing description, a common signal pre-amplifier SA is associated with the three signal channels K1, K2, K3, and the sensing signal S from the yarn sensing device 5, FIG. 1, is delivered to that pre-amplifier SA. The signal channel Kl further comprises a pulse amplitude modulator PAMl one input of which is connected to the output of the signal pre-amplifier SA and another input of which is supplied with the control signal C. In PAMl the pulsed control signal C is mixed multiplicatively with the sensing signal S. The output signal of PAMI is a pulse train which, with fixed potential VC, is modulated with the amplitude of the sensing signal S. The output signal pulse train of PAMl is demodulated in a following demodulator DEM l, and the demodulated signal from DEM 1 is led to an output amplifier EA 1. Up to this output amplifier, the three channels of the processor 1 have similar general structures, however, different amplifications and differently designed output amplifiers.

The output stage of the C-channel comprises a low pass filter TP which passes only signals of a relatively long duration corresponding to a running yarn length of some decimeters. Connected to the output of the low pass filter T? is one input of the threshold discriminator DI which is common to the C-, N- and D-channels. The output of the threshold discriminator DI is connected to the yarn severing device 4, FIG. 1.

The output stage of the D-channel comprises a length measuring circuit LM which produces a length signal which represents the length of a yarn section the diameter of which exceeds a fixed value which is pre-set at the potentiometer D. The length scale of the length measuring circuit LM can be controlled by means of a potential L which is supplied to a second input of that circuit from a further'setting device not shown in the Figures.

For the N- and D-channels is provided a common analog calculator, e.g. an adder or multiplier circuit DN having two inputs to which the output signals of the N- and D-channels are led. In the analog calculator DN the said output signals are combined functionally, e.g. added according to the present embodiment. The combination signal generated by DN is delivered to-a secand input of the threshold discriminatorDI which, by way of example, is a monostable' mutlivibrator or 'monoflop. I

The electronic setting and checking apparatus 2 represented in the lower part of FIG. 2 comprises the channel selector 6 provided with a three-way changeover switch KS each 'of the fixed contacts of which is connected individually with an output of one of the control channels S1, S2, S3 over a removable cable not shown in FIG. 2. The d.c. amplifier channel 7 comprises, as an input stage, a signal differential amplifier SD having a signal input terminal A and a compensation input terminal K. One input terminal E of a pulse amplitude modulator PAM 2 is connected to the output of the differential amplifier SD and a second input ter-- minal B of PAM 2 is connected electrically with the contact arm CA of the change over-switch KS so that depending upon the setting ofthe latter one of the control signals C, N, D is delivered to the second input terminal B of PAM 2. To th'e output of PAM 2 is connected a demodulator DEM 2, and to the output of the latter a changeable output amplifier EA 2 is connected which comprises a three-way change-over switch device which is not'shown and, which is connected mechanically with the contact arm CA of KS as indicated by the line F-F, so that the amplification existing in the d.c. amplifier channel 7 corresponds, with each position of contact arm CA,to the amplificationexisting in the associated signal channel of the signal processor 1. According to the present exemplified embodiment the d.c.,amplifier channel 7 is not-designed as a d.c. amplifier in a restricted meaning of this term, however it operates as'such, with respect to the sensing signal S', because of the multiplicative mixture in PAM 2 and the following demodulation in- DEM '2. The d.c. amplifier channel 7 may be replaced by an a.c. amplifier having a very low lower cutoff frequency, e.g. 0.01 cycles per second. However, in this case, the time intervals in which measurements are made should be rather short.

A negative feedback loop arranged as a compensating and holding circuit is connected between the output of the differential amplifier SD and the second input terminal K of same. The feedback loop serves for compensating the d.c. component of the sensing signal S which is produced with no yarn present or on inserting a yarn having a fixed standard diameter into the yarn sensing device 5, and the drift of the differential amplifier SD. Such a compensation is advantageous since the level of d.c. component normally is by far greater than the amplitudes of the signals representing the yarn diameters and/or imperfections. The input of the compensating and holding circuit 9 may also be connected to some other point of the d.c. amplifier channel 7 following the signal differential amplifier SD, e.g. the output 0 of same. The negative feedback loop 9 comprises an input amplifier stage RA, a holding condenser HC and an impedance transformer IS the input of which comprises a field efiect transistor FET whose gate is connected to one electrode of the holding condenser l-IC. A closing switch OS is arranged between the output of input amplifier stage RA and the mentioned electrode of holding condenser BC. The closing switch OS is preferably a push botton switch. The input amplifier stage RA should have a high voltage amplification, e.g. 1000. A high grade holding condenser I-IC is to be used in order that the feedback potential provided by RA to the condenser I-IC when closing switch OS can be maintained for a long time without substantial loss after'opening switch OS. The impedance transformer IS provided with field effect transistor FET also prevents, by its extremely high input impedance,-lacking of the electrical charge existing at BC. The negative feedback loop 9 delivers a compensation potential K to the second input terminal K of the signal differential amplifier SD and thus provides for a substantially complete cancellation of the d.c. component of the signal present at the output of SD. In order to bring the negative feedback loop into action the switch OS is closed prior to each measurement and kept closed until after complete compensation has occurred. This is realized when thereading ofindicating device 8 has reached the zero position. Now when OS is opened, because of the action of holding condenser HC the compensation is maintained during a relatively long time interval during which a measurement may be carried out in a manner to be explained with reference to FIG. 3 in the description tofollow.

The equipment shown in FIG. 3 comprises the devices as already described in connection with FIG. 1, i.e. the electronic signal processor 1, the electronic setting and checking apparatus 2, a sensing head compris-- ing a yarn severing device 4 and an electro-optical yarn sensing device 5, and additionally a yarn moving device 10 mounted on a base plate 1 ii. A bobbin'support l2 fixed at one end of the base plate l1 carries a yarn supply bobbin 13. A yarn pull-off device 14 is located near the opposite end of base plate 11, thereon..The yarn pull-off device 14 comprises a bearing support l7,a pair of rollers 19 and aidrive means 20 comprising, by way of example, a crank handle to be operated manually. Alternatively, an electric motor may be provided as a drive means. The sensing head 4,5 provided with a yarn guide groove 15 is mounted by means of a bracket 16 on the base plate 11 between the bobbin support 12 and the yarn pull-off device 14. Further, a yarn insertion device 21 is provided on base plate 11 which enables the yarn l8 drawn off the bobbin 13 to be inserted in the yarn guide groove 15 of the feeler head 4,5. The yarn insertion device 21 comprises a bearing block 25, a shaft 22 tiltably mounted on bearing block 25, and two insertion arms 23 which are fixedly attached to shaft 22. Each insertion arm 23 is provided with a groove 24 for guiding the yarn 18. Fixed to the rear part of base plate 1 1 is a panel 26 carrying the signal processor 1 and the setting and checking apparatus 2 so that the complete equipment forms a structural unit.

The equipment shown in FIG. 3 is designed for finding the correct or desirable setting of a yarn clearer system mounted in a winding or spinning plant, with respect to a certain yarn to be cleared therewith, by carrying out a preliminary test outside the winding or spinning plant, e.g. in a special laboratory. Such a yarn clearer system may comprise a common central control device containing several signal channels, e.g. three signal channels S1, S2, S3 as illustrated in the left upper part of FIG. 2, and a plurality of signal amplifiers and feeler heads (see FIG. 1, feeler head 3), each feeler head being associated with an individual signal amplifier comprising signal channels, e.g. three signal channels K1, K2, K3 as shown in the right upper part of FIG. 2, one feeler head and signal amplifier being arranged at each winding or spinning location. By using the equipment shown in FIG. 3, the winding trials which otherwise are to be made in winding and spinning plants and which are based on the employment of winding or spinning machines and the sometimes substantial time losses caused by such trials in the plants can be avoided.

Now a setting procedure with the equipment of FIG. 3 for one of the channels of processor 1, e.g. the C- channel, will be explained. This so-called double yarn channel is designed for eliminating, together with the yarn sensing head, yarn sections having a cross sectional area of at least twice the mean cross sectional area of the normal yarn and a length of at least 50 cm. The diameter of such a yarn section is at least 1,4 (i.e. 2 times the normal yarn diameter.

Since the full scale reading at MS, FIG. 2 of the indicating device 8 should correspond to the threshold response of the C-channel, a reading of about 70 percent full scale (i.e. full scale reading: 1,4) corresponds to the mean normal yarn diameter.

The setting of the C-channel may be carried out in a simple manner as follows:

I. The'switch K8 is set to the C-channel position. Since at the beginning the severing device 4 must not be actuated, it is inactivated, e.g. by means of a break switch which is not shown in FIG. 3.

2. A yarn 18 having normal diameter is drawn from supply bobbin 13, inserted in the grooves 24 of yarn insertion device 21, howevernot yet introduced in the yarn guide groove 15 of the yarn feeler head 4,5, and further drawn through the pair of rollers 19.

3. Closing button OS is pressed and held down until indicating device 8 shows zero reading, whereupon OS is released.

4. Yarn 18 is introduced into the guide groove 15 of feeler head 4,5 and drawn through same by actuat ing crank handle 20. Indicating device 8 now shows a positive reading. The C-setting device in processor 1 is then adjusted in such a manner that the indication is percent full scale reading, which position is marked by index mark M in FIG. 2 at the scale of indicating device 8. Thereupon, the setting of the C-channel is completed.

As a check test, a double yarn sample made by twisting two single yarns 18 together may be inserted into the yarn guide groove instead of the single yarn; therewith, full scale reading should appear on the indicating device 8, and the yarn severing device 4 on activating same should respond.

The D-channel may be adjusted in a similar manner, however, the threshold response should occur in this case at another diameter, e.g. twice the normal yarn diameter. With the N-channel, i.e. the so-called nep channel, the threshold response should occur at a substantially higher value, e.g. five times the normal yarn diameter.

The values of the parameters C, D, N etc. determined by such preliminary trials may be transferred to the setting device or devices comprised by the yarn clearer systems in a winding or spinning plant which are not shown in FIG. 3.

The above described setting procedure relies on measuring the mean diameter of a sample of the yarn to be cleared. This becomes evident from the foregoing description under number 4: when the setting of the C- channel is made correctly, the running yarn causes a reading of 70 percent full scale indication to appear on indicating device 8. With the running yarn the reading fluctuates, because of the unavoidable irregularity of the yarn, about a mean value which is labeled by the index mark M. When the measurement is extended over a sufficiently long time interval, that means over a sufficiently great yarn length, a reliable mean value of the yarn diameter is provided.

The known setting procedures mentioned in the introduction make use of a parameter, eg the yarn count, which is a measure of a transversal dimension of the yarn and which has been defined by conventional methods. With the present new procedure, a transversal dimension measured with the help of a yarn sensing device is taken as a basis for setting a yarn clearer system provided with similar yarn sensing devices so that a better accuracy results. Moreover, the setting errors which may occur when the corrections mentioned in the introduction are effected, are avoided with the present procedure.

Further on, the new setting procedure affords particular benefits when clearing analogous yarns, i.e. yarns which difi'er only by their transversal dimensions whereas their other properties are alike. Within a group of such yarns, for any yarn the values of the parameter C, D, N etc. can be used which have been determined by measuring one of the yarns. Thereafter, for any other yarn of the group only the mean diameter or other transversal dimension need be determined. However, this application of the new setting procedure requires the properties of the yarns in question insofar as the clearing effect depends on them to have a certain degree of regularity so that these yarns can be arranged in a certain group; for any yarn in the group the same relation between the diameter of an irregularity which corresponds to the threshold response, and the normal or mean diameter of the yarn is taken as existmg.

With a modification of the new setting procedure, it is possible to proceed from given limiting irregularities, i.e. yarn irregularities the diameter of which sets the limit at which the clearing effect is to be brought into action. In this case, after inserting a limiting irregularity into the yarn sensing device 4, the setting device, e.g. N, is adjusted in such a manner that the indicating device 8 shows full scale reading at'MS, FIG. 2, in order to introduce the desired threshold response into the corresponding signal channel.

In the embodiment shown in FIG. 1 the channel selector 6, the testing contact 27 and the testing signal source 28 are provided for successive measurements or tests of the various functions of a yarn'clearer. Alternatively, testing and setting a multichannel yarn clearer may be made simultaneously after connecting one individual electronic setting and checking apparatus 2 in series which each of the control channels 81, S2, S3, FIG. 2. In this case the channel selector 6 may be dispensed with. Moreover, a testing contact 27 and a testing signal source 28 are dispensable parts of the setting and checking apparatus 2 when a testing signal is led from outside to the input terminal A of the d.c. amplifier channel 7, after removing the connection with the yarn sensing device 5. However, the presence of the testing contact 27 and testing signal source facilitate the testing and afford no essential additional expenditure.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Accordingly, what is claimed is: 1. In an electronic yarn clearer system including means for sensing a yarn contactlessly and for providing a sensing signal, and signal processing means operatively connected to the output of said yarn sensing means, the signal processing means comprising at least one controllable processing channel including a control channel and a signal amplifying channel controllably connected to the control channel, and further comprising threshold discriminating means operatively connected in series with said signal amplifying channel;

at least one electronic checking means comprising a controllable amplifying channel having a signal input terminal connectable with the output of the yarn sensing means, and a control input terminal connectable to the output of said control channel for producing an output signal representing a transversal dimension of the yarn;

means connected to the controllable amplifying channel for compensating a signal level representing the constant base signal of said sensing signal; and

indicating means connected to the output of the controllable amplifying channel for producing an indication representative of the value of said output signal.

2. The electronic checking means as defined in claim I, wherein said controllable amplifying channel is a d.c. amplifying channel.

3. The electronic checking means as defined in claim 2, wherein the controllable d.c. amplifying channel comprises a pulse amplitude modulating means for multiplicatively mixing the sensing signal with a control signal in pulsed shape generated by said control channel.

4. The electronic checking means as defined in claim 1, wherein the controllable amplifying channel comprises a signal differential amplifier, a pulse amplitude modulator having a first input terminal connected with the output of said differential amplifier and a second input terminal identical with said control input terminal, a demodulator connected in series with the output of said pulse amplitude modulator, and an output amplifier the input of which is connected to the output of said demodulator.

5. The electronic checking means as defined in claim 1, wherein the compensating means is arranged as a negative feedback loop operatively coupled to said controllable amplifying channel, and includes an input amplifier stage, a holding condenser, a closing button for connecting temporarily one electrode of the holding condenser to the output of the input amplifier stage, and an impedance transformer output stage the input of which comprises a field effect transistor whose gate is connected to said one electrode of the holding condenser.

6. The electronic checking means as defined in claim 1, further comprising a plurality of control channels and a channel selector for selectively connecting the output of one .of the control channels to said control input terminal.

7.- The electronic checking means as defined in claim 1, further comprising a testing signal source and testing contact means for selectively connecting the signal input tenninal to the output of said yarn sensing means or the testing signal source.

8. The electronic checking means as defined in claim 1, wherein the indicating means comprises at least one index mark for defining an indication which corresponds to a fixed fraction of the value of the sensing signal-to which the threshold discriminating means is responsive.

9. The electronic checking means as defined in claim 1, which is arranged as a self-contained unit.

10. Equipment for setting and checking an electronic.

yarn clearer system, including means for sensing a yarn contactlessly and for providing a sensing signal; signal processing means operatively connected to the output of said sensing means, the signal processing means comprising at least onecontrollable processing channel including a control channel and a signal amplifying channel controllably connected to the control channel,

and further comprising threshold discriminatingmeans operatively connected in series with said signal c hannel;

at least one electronic checking means comprising a controllable d.c. amplifying channel having a signal input terminal connectable with the output of the yarn sensing means, and a control input terminal connectable to the output of a control channel for representative of the value of said output signal; and

further comprising means for moving a length of yarn continuously through the yarn sensing means.

11. The equipment as defined in claim 10, wherein the yarn moving means comprises a bobbin support for receiving a yarn supply bobbin, means for pulling yarn off the yarn supply bobbin and through said yarn sensing means, and wherein means are provided for inserting into and removing from said yarn sensing means a length of yarn passing from the supply bobbin to the yarn pull-off means. v

12. The equipment as claimed in claim 10, wherein the yarn sensing means, the signal processing means, the electronic checking means and the yarn moving means are assembled into a portable structural unit.

13. An electronic apparatus for setting and checking electronic yarn clearer systems, comprising a controllable d.c. amplifying channel having a signal input terminal and at least one control input terminal; a negative feedback loop operatively coupled to said controllable d.c. amplifying channel and including an input d.c. amplifier stage, a holding condenser, a closing button for connecting temporarily one electrode of the holding condenser to the output of the input d.c. amplifier stage, and an impedance transformer output stage the input of which comprises a field effect transistor whose gate is connected to said one electrode of the holding condenser; and indicating means connected to the out put of the controllable d.c. amplifying channel for producing an indication representative of the value of the output signal of the d.c. amplifying channel.

l I. I III 

1. In an electronic yarn clearer system including means for sensing a yarn contactlessly and for providing a sensing signal, and signal processing means operatively connected to the output of said yarn sensing means, the signal processing means comprising at least one controllable processing channel including a control channel and a signal amplifying channel controllably connected to the control channel, and further comprising threshold discriminating means operatively connected in series with said signal amplifying channel; at least one electronic checking means comprising a controllable amplifying channel having a signal input terminal connectable with the output of the yarn sensing means, and a control input terminal connectable to the output of said control channel for producing an output signal representing a transversal dimension of the yarn; means connected to the controllable amplifying channel for compensating a signal level representing the constant base signal of said sensing signal; and indiCating means connected to the output of the controllable amplifying channel for producing an indication representative of the value of said output signal.
 2. The electronic checking means as defined in claim 1, wherein said controllable amplifying channel is a d.c. amplifying channel.
 3. The electronic checking means as defined in claim 2, wherein the controllable d.c. amplifying channel comprises a pulse amplitude modulating means for multiplicatively mixing the sensing signal with a control signal in pulsed shape generated by said control channel.
 4. The electronic checking means as defined in claim 1, wherein the controllable amplifying channel comprises a signal differential amplifier, a pulse amplitude modulator having a first input terminal connected with the output of said differential amplifier and a second input terminal identical with said control input terminal, a demodulator connected in series with the output of said pulse amplitude modulator, and an output amplifier the input of which is connected to the output of said demodulator.
 5. The electronic checking means as defined in claim 1, wherein the compensating means is arranged as a negative feedback loop operatively coupled to said controllable amplifying channel, and includes an input amplifier stage, a holding condenser, a closing button for connecting temporarily one electrode of the holding condenser to the output of the input amplifier stage, and an impedance transformer output stage the input of which comprises a field effect transistor whose gate is connected to said one electrode of the holding condenser.
 6. The electronic checking means as defined in claim 1, further comprising a plurality of control channels and a channel selector for selectively connecting the output of one of the control channels to said control input terminal.
 7. The electronic checking means as defined in claim 1, further comprising a testing signal source and testing contact means for selectively connecting the signal input terminal to the output of said yarn sensing means or the testing signal source.
 8. The electronic checking means as defined in claim 1, wherein the indicating means comprises at least one index mark for defining an indication which corresponds to a fixed fraction of the value of the sensing signal to which the threshold discriminating means is responsive.
 9. The electronic checking means as defined in claim 1, which is arranged as a self-contained unit.
 10. Equipment for setting and checking an electronic yarn clearer system, including means for sensing a yarn contactlessly and for providing a sensing signal; signal processing means operatively connected to the output of said sensing means, the signal processing means comprising at least one controllable processing channel including a control channel and a signal amplifying channel controllably connected to the control channel, and further comprising threshold discriminating means operatively connected in series with said signal channel; at least one electronic checking means comprising a controllable d.c. amplifying channel having a signal input terminal connectable with the output of the yarn sensing means, and a control input terminal connectable to the output of a control channel for producing an output signal representing a transversal dimension of the yarn; means connected to the controllable d.c. amplifying channel for compensating for a signal level representing the constant base signal of said sensing signal; means connected to the output of the controllable d.c. amplifying channel for producing an indication representative of the value of said output signal; and further comprising means for moving a length of yarn continuously through the yarn sensing means.
 11. The equipment as defined in claim 10, wherein the yarn moving means comprises a bobbin support for receiving a yarn supply bobbin, means for pulling yarn off the yarn supply bobbin and through said yarn sensing means, and wherein means are pRovided for inserting into and removing from said yarn sensing means a length of yarn passing from the supply bobbin to the yarn pull-off means.
 12. The equipment as claimed in claim 10, wherein the yarn sensing means, the signal processing means, the electronic checking means and the yarn moving means are assembled into a portable structural unit.
 13. An electronic apparatus for setting and checking electronic yarn clearer systems, comprising a controllable d.c. amplifying channel having a signal input terminal and at least one control input terminal; a negative feedback loop operatively coupled to said controllable d.c. amplifying channel and including an input d.c. amplifier stage, a holding condenser, a closing button for connecting temporarily one electrode of the holding condenser to the output of the input d.c. amplifier stage, and an impedance transformer output stage the input of which comprises a field effect transistor whose gate is connected to said one electrode of the holding condenser; and indicating means connected to the output of the controllable d.c. amplifying channel for producing an indication representative of the value of the output signal of the d.c. amplifying channel. 